1. Field of Invention
This invention relates to a method for predicting when a consumable unit should be replaced.
2. Description of Related Art
The photocopier industry modularizes a variety of consumable components as disposable cartridges, categorized by function, employed in the photocopier machine. Each of these cartridges to be inserted or removed from the machine constitutes a replaceable cartridge, designated in portions of the industry as a customer replaceable unit (CRU), for example, as described in U.S. Pat. No. 5,809,375 to Owens Jr. et al. and U.S. Pat. No. 6,173,128 to Saber et al. For example, a color photocopier may include a total of ten CRUs: four photoreceptor cartridges for each color separation cyan, magenta, yellow and black (CMYK) to be imaged, developed and transferred, four toner cartridges for each color to be developed, a second black toner cartridge, and a fuser cartridge for heating and fixing the image to the sheet.
An electronically erasable programmable read-only-memory (EEPROM) may be used to store identifier and status information for the CRU that is readable by a microprocessor in the machine. Integrated with the CRU, the EEPROM thus comprises a CRU monitor (CRUM), for example, as described in U.S. Pat. No. 5,272,503 to LeSueur et al. The CRUM provides identification to the microprocessor to enable verification that the model and configuration of the CRU is compatible and appropriate for use with the machine. This information can include pricing arrangements to distinguish CRUs intended for metered (flat-rate) contracts and pay-as-you-go orders, or regional designations to avoid arbitrage (use in an unintended market).
The CRUM also accumulates integer counts related to usage of the corresponding CRU. For each scanned image, for example, a photoreceptor CRU rotates its drum or belt for a design number of rotation cycles. Each cycle can be counted and accumulated in a photoreceptor CRUM. In another example, a printhead in a toner cartridge, ejects a quantity of ink (fluid) for each pixel. (Similarly, a xerographic device deposits a quantity of toner onto an electrostatically charged drum.) An ink (toner) CRUM counts and accumulates each ink ejection event by the printhead, for example, as described in U.S. Pat. No. 5,636,032 to Springett.
The photoreceptor can be operated for a design number of cycles before wear decreases reliability below an acceptable level, thus compromising print quality. When the number of cycles operated by the photoreceptor and counted by the photoreceptor CRUM exceeds a programmed threshold or end point, the microprocessor can signal the user that replacement is necessary. Similarly, a toner cartridge maintains a volume of toner material, which is consumed in the process of printing. When the number of print operations (or pixels) counted by the toner CRUM exceeds a threshold established for that toner model, the microprocessor can signal the user that the toner material in its reservoir is near depletion.